Vehicle brake system

ABSTRACT

A vehicle brake system is provided with a hydraulic brake device, a regenerative brake device incorporating a generator motor, and a brake control device. The control device includes a section for calculating a driver target brake force for each wheel corresponding to a manipulation amount of a braking manipulation member, a section for enabling the brake control device itself to set compensation brake forces for respective wheels, a section for selecting a larger one of the driver target brake force and the compensation brake force for each wheel and for subtracting a base hydraulic brake force from the selected brake force to set differences for respective wheels as compensated target brake forces for the wheels, and a section for controlling the distribution of the compensated target brake force for each wheel to a controlled hydraulic brake force for each wheel and a regenerative brake force for each driving wheel.

INCORPORATION BY REFERENCE

This application is based on and claims priority under 35 U.S.C. 119with respect to Japanese Application No. 2010-213201 filed on Sep. 24,2010, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle brake system provided with ahydraulic brake device and a regenerative brake device. Moreparticularly, it relates to a brake control device for cooperativelycontrolling the hydraulic brake device and the regenerative brakedevice.

2. Discussion of the Related Art

In hybrid vehicles which are provided with an engine and a generatormotor as travelling drive sources, it has become widespread to heightenthe fuel efficiency by regenerating motion energy to electric energy bythe generator motor and storing the electric energy at the time of abraking operation. In this sense, the generator motor is regarded as aregenerative brake device that applies the regenerative brake force todriving wheels. The regenerative brake device alone is unable togenerate a sufficient brake force and thus, is usually used incombination with a conventional hydraulic brake device which operatesunder pressurized oil. Therefore, a cooperative control is required forthe hydraulic brake device and the regenerative brake device, and therehave been proposed various cooperative control technologies like thatdescribed in US 2007/0272457 A1 (equivalent of JP2007-308005 A).

A vehicle disclosed in the United State publication is provided with acombustion engine, an electric motor, battery means, fluid-operatedbrake means (hydraulic brake device), demand brake force setting means,and brake control means. The fluid-operated brake means is able tooutput a brake force based on a manipulation pressure (base hydraulicpressure), corresponding to the driver's manipulation and a negativepressure in the combustion engine, and an additional pressure(controlled hydraulic pressure) given by pressurizing means. Further,when a brake demand manipulation is performed, the brake control meansexecutes a control to compare a sum of a regenerative brake force by theelectric motor and a manipulation brake force corresponding to themanipulation pressure with a demand brake force and judges the necessityof a brake force depending on the additional pressure. The control makesit possible that even when the negative pressure in the combustionengine goes down, a demand brake force is acquired correctly bysuppressing an uncomfortable feeling which is liable to be felt by thedriver.

Further, although the hydraulic brake device usually operates inresponse to the braking manipulation by the driver and, in addition tothis function, is often to have a function of automatically adjustingthe brake force to be increased or reduced. Such an automatic brakecontrol function is realized in a combination of an electronic controldevice, incorporating a computer and being operable by software, andsensors for acquiring various information such as braking manipulationamount, wheel speeds and the like. For example, in an active cruisecontrol (ACC) function, a following distance (i.e., a distance to avehicle ahead) is kept to be longer than a predetermined value bygenerating a brake force in dependence on the situation where a brakingmanipulation is not performed or the amount of the braking manipulationis insufficient though a detected following distance decreases. In abrake assist (BA) function, it is discriminated based on a brakingmanipulation amount and a manipulation speed whether or not a brakingmanipulation is an urgent braking manipulation, and an additional brakeforce is added to the brake force corresponding to the brakingmanipulation force. Further, in an antilock brake system (ABS) function,when a wheel is locked at the time of an urgent braking manipulation,the hydraulic pressure in the hydraulic brake device is automaticallyadjusted to regulate the brake force thereby to suppress the slipping ofthe wheel. Those belonging to this category are a traction control (TRC)function that controls the driving force to be effectively exerted onthe road surface by adding a brake force when the slipping amounts ofthe driving wheel are large, and an electronic stability control (ESC)function that keeps the stability in travelling by regulating thebraking amounts of respective wheels during the travelling.

In systems provided with a hydraulic brake device and a regenerativebrake device as typically described in the aforementioned United Statepublication, when a braking manipulation is done, the regenerative brakedevice is additionally operated whereas, during an automatic brakecontrol function such as the ACC function, the BA function or the like,the brake force is regulated only by the hydraulic brake device with theregenerative brake device held out of operation. That is, a stage thatthe regenerative brake function by a generator motor can be utilizedtakes place unless the driving wheels are being driven when the brakeforce is generated by the automatic brake control function. However,during the automatic brake control function, the regenerative brakefunction has heretofore not been utilized for the reason that theutilization of the regenerative brake function at that stage complicatesthe distribution of brake forces to respective wheels, and the like. Asa result, the hydraulic brake device only has been used even at thestage that the regenerative brake device can be inherently utilized, andthus, the opportunity to enhance the efficiency in regeneration has beenlost.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providean improved vehicle brake system which when generating a brake force byan automatic brake control function, is able to distribute a part of thebrake force to a regenerative brake device, thereby enhancing theefficiency in regeneration.

Briefly, in a first aspect of the present invention, there is provided avehicle brake system, which comprises a hydraulic brake device having amaster cylinder for generating a base hydraulic pressure correspondingto a manipulation amount of a braking manipulation member, a pump forgenerating a controlled hydraulic pressure, and a hydraulic control unitfor adding a base hydraulic brake force corresponding to the basehydraulic pressure and a controlled hydraulic brake force correspondingto the controlled hydraulic pressure to apply the added brake forces towheels; a regenerative brake device for applying a regenerative brakeforce to driving wheels which are included in the wheels and are drivenby a generator motor; and a brake control device for cooperativelycontrolling the hydraulic brake device and the regenerative brakedevice. The brake control device includes a driver target brake forcecalculation section for calculating a driver target brake force for eachwheel corresponding to the manipulation amount of the brakingmanipulation member; a compensation brake force setting section forenabling the brake control device to set compensation brake forces forthe respective wheels independently of the driver target brake force; aselection compensation section for selecting a larger one of the drivertarget brake force and the compensation brake force for each wheel andfor subtracting the base hydraulic brake force from the selected onebrake force to set a compensated target brake force for each wheel; anda distribution control section for controlling the compensated targetbrake force for each wheel to be distributed to the controlled hydraulicbrake force for each wheel and the regenerative brake force for eachdriving wheel.

With the construction in the first aspect of the present invention, thebrake control device which cooperatively controls the hydraulic brakedevice and the regenerative brake device selects a larger one of thedriver target brake force corresponding to the manipulation amount ofthe braking manipulation member and the compensation brake force set bythe brake control device itself for each wheel, subtracts the basehydraulic brake force from the selected one brake force to set acompensated target brake force for each wheel, and distributes thecompensated target brake force to the controlled hydraulic brake forcefor each wheel and the regenerative brake force for each driving wheel.Thus, when the compensation brake force exceeds the driver target brakeforce, at least a part of the brake force which part corresponds to asurplus is distributed to the regenerative brake device. This results inbringing the regenerative brake device into operation though the samehas heretofore not been operated when the compensation brake forces setby the brake control device itself are generated during an active cruisecontrol function or the like, and therefore, the efficiency inregeneration can be enhanced.

In a second aspect of the present invention, there is provided a vehiclebrake system, which comprises a hydraulic brake device having a mastercylinder for generating a base hydraulic pressure corresponding to amanipulation amount of a braking manipulation member, a pump forgenerating a controlled hydraulic pressure, and a hydraulic control unitfor adding a base hydraulic brake force corresponding to the basehydraulic pressure and a controlled hydraulic brake force correspondingto the controlled hydraulic pressure to apply the added brake forces towheels; a regenerative brake device for applying regenerative brakeforces to driving wheels which are included in the wheels and are drivenby a generator motor; and a brake control device for cooperativelycontrolling the hydraulic brake device and the regenerative brakedevice. The brake control device includes a driver target brake forcecalculation section for calculating a driver target brake force for eachwheel corresponding to the manipulation amount of the brakingmanipulation member; a compensation brake force setting section forenabling the brake control device itself to set compensation brakeforces for the respective wheels independently of the driver targetbrake force; an addition compensation section for adding thecompensation brake force for each wheel to the driver target brake forceto obtain a sum and for subtracting the base hydraulic brake force fromthe sum to set a compensated target brake force for each wheel; and adistribution control section for controlling the compensated targetbrake force for each wheel to be distributed to the controlled hydraulicbrake force for each wheel and the regenerative brake force for eachdriving wheel.

With the construction in the second aspect of the present invention, thebrake control device which cooperatively controls the hydraulic brakedevice and the regenerative brake device adds the driver target brakeforce corresponding to the manipulation amount of the brakingmanipulation member and the compensation brake force set by the brakecontrol device itself for each wheel to obtain the sum, subtracts thebase hydraulic brake force from the sum to set the compensated targetbrake force for each wheel, and distributes the compensated target brakeforce to the controlled hydraulic brake force for each wheel and theregenerative brake force for each driving wheel. Thus, at least a partof the compensation brake force is distributed to the regenerative brakedevice. This results in bringing the regenerative brake device intooperation though the same has heretofore not been operated when thecompensation brake forces set by the brake control device itself aregenerated during a brake assist function or the like, and therefore, theefficiency in regeneration can be enhanced.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The foregoing and other objects and many of the attendant advantages ofthe present invention may readily be appreciated as the same becomesbetter understood by reference to the preferred embodiments of thepresent invention when considered in connection with the accompanyingdrawings, wherein like reference numerals designate the same orcorresponding parts throughout several views, and in which:

FIG. 1 is a schematic view showing the construction of a vehicle brakesystem in a first embodiment according to the present invention;

FIG. 2 is a circuit diagram showing the detailed construction of ahydraulic brake device shown in FIG. 1;

FIG. 3 is a graph showing the operation property at an ordinary time ofthe vehicle brake system;

FIG. 4 is a flow chart showing a control processing executed by a brakeECU in the first embodiment;

FIG. 5 is a combination of graphs schematically exemplifying the resultthat the brake ECU attains in the control processing shown in FIG. 4during the operation of an active cruise control function;

FIGS. 6(A)-6(D) are schematic diagrams for explaining specific examplesof distribution controls in which a left right equal-time distributioncontrol means or section executes the distribution of brake forces torespective wheels;

FIGS. 7(A)-7(B) are schematic diagrams for explaining specific examplesof distribution controls in which a left right unequal-time distributioncontrol means or section executes the distribution of brake forces tothe respective wheels;

FIG. 8 is a flow chart showing a control processing executed by thebrake ECU in a second embodiment; and

FIGS. 9(A)-9(D) are explanatory views for showing specific examples ofdistribution controls in which brake forces are distributed to therespective wheels in the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereafter, a vehicle brake system in a first embodiment according to thepresent invention will be described with reference to FIGS. 1-7. FIG. 1is a schematic view showing the construction of a vehicle brake system 1in the first embodiment according to the present invention. As shown inthe figure, the vehicle brake system 1 is composed of a regenerativebrake device A, a hydraulic brake device B, a hybrid ECU 50, a brake ECU60 and the like. The vehicle brake system 1 is equipped on afront-drive, four-wheel hybrid vehicle and is usually operated independence on a stepping manipulation of a brake pedal 21 by the driver.In addition thereto, the system 1 has a function in which the brake ECUautomatically sets and regulates a brake force for each wheel independence on the vehicle travelling state.

The regenerative brake device A is constituted by a generator motor 20incorporated therein and includes an inverter device and a batterydevice (both not shown). The generator motor 20 operates as electricmotor by being driven by the inverter device which converts a directcurrent voltage of the battery device into an alternating currentvoltage, and drives a front right wheel 7FR and a front left wheel 7FLboth being driving wheels. Further, the generator motor 20 operates asgenerator by being driven by the front right wheel 7FR and the frontleft wheel 7FL and charges the battery device through the inverterdevice. At this time, the reaction force from the generator motor 20applies a regenerative brake force to the front right wheel 7FR and thefront left wheel 7FL, and thus, this function is generally called theregenerative brake device A. The front right wheel 7FR and the frontleft wheel 7FL are on a common axle connected to the generator motor 20and thus, generate regenerative brake forces which are almost the samein strength. In a modified form, a generator and an electric motor maybe individually provided in substitution for the generator motor 20, andthe generator may be provided with the function of operating as theregenerative brake device A.

The hybrid ECU 50 is an electronic controller for controlling the wholeof a power train for the hybrid vehicle and cooperatively controls anengine (not shown) and the generator motor 20. The hybrid ECU 50 isconnected to the inverter device and controls the regenerative brakedevice A.

The hydraulic brake device B uses operating oil as operating fluid andas shown therein, is composed of a brake pedal 21, a vacuum brakebooster 22, a master cylinder 23, a hydraulic control unit 25 and thelike. In the hydraulic brake device B, the stepping force given by thestepping manipulation of the brake pedal 21 is boosted by the vacuumbooster 22, a base hydraulic pressure is generated by operating themaster cylinder 23, and a controlled hydraulic pressure is added to thebase hydraulic pressure by operating pumps 37, 47 (FIG. 2) in thehydraulic control unit 25, so that the hydraulic pressure so added isapplied to respective wheel cylinders WC2, WC3, WC4 and WC1 of the frontright wheel 7FR, the front left wheel 7FL, a rear right wheel 7RR and arear left wheel 7RL. Hereafter, the hydraulic brake device B will bedescribed in detail with reference to FIG. 2.

FIG. 2 is a circuit diagram showing the detailed construction of thehydraulic brake device B shown in FIG. 1. The brake pedal 21 is a membercorresponding to a braking manipulation member and operates the vacuumbooster 22 in correspondence to the stepping manipulation amount. Astroke amount being the manipulation amount of the brake pedal 21 isdetected by a pedal stroke sensor 21a and is outputted as detectionsignal to the brake ECU 60. The vacuum booster 22 boosts the steppingforce by the stepping manipulation of the brake pedal 21 by utilizing anegative pressure supplied from the engine (not shown) and operates themaster cylinder 23.

The master cylinder 23 is of a tandem type and is constituted by ahousing 23 a taking the shape of a bottomed cylinder and first andsecond pistons 23 b, 23 c arranged in line in the housing 23 a to befluid-tightly and slidably. A first hydraulic chamber 23 d is formedbetween the first piston 23 b and the second piston 23 c, while a secondhydraulic chamber 23 f is formed between the second piston 23 c and abottom portion of the housing 23 a. The first and second pistons 23 b,23 c are driven by the vacuum brake booster 22 to generate a basehydraulic pressure in the first and second hydraulic chambers 23 d, 23f. Further, a reservoir 24 has a function of regulating the quantitiesof the operating oil in the first and second hydraulic chambers 23 d, 23f by communicating with the same when the first and second pistons 23 b,23 c are not being operated.

The hydraulic control unit 25 is constructed by packaging into a singlecase hydraulic control valves 31, 41; pressure increase control valves32, 33, 42, 43 and pressure reducing control valves 35, 36, 45, 46 whichconstitutes ABS control valves; pressure regulating reservoirs 34, 44;pumps 37, 47; and a motor M. As shown in FIG. 2, the brake pipingpassage of the hydraulic brake device B in the present embodiment isconfigured to take an X-piping fashion which has a first piping passageL1 for applying a hydraulic brake force to the front right wheel 7FR andthe rear left wheel 7RL and a second piping passage L2 for applying thehydraulic brake force to the front left wheel 7FL and the rear rightwheel 7RR. The master cylinder 23 is connected to the second pipepassage L2 at the first hydraulic chamber 23 d and to the first pipingpassage L1 at the second hydraulic chamber 23 f.

First of all, description will be made regarding the construction of thefirst piping passage L1 of the hydraulic control unit 25. The firstpiping passage L1 is provided thereon with the hydraulic control valve31 constituted by a differential pressure control valve. The hydrauliccontrol valve 31 is switchable into a communication state and adifferential pressure state in response to a command from the brake ECU60. The hydraulic control valve 31 is usually held in the communicationstate, but by being switched into the differential pressure state, isable to maintain an oil passage L12 on the wheel cylinder WC1, WC2 sidesat a pressure which is higher by a predetermined differential pressurethan the base hydraulic pressure of an oil passage L11 on the mastercylinder 23 side. This differential pressure is a controlled hydraulicpressure and can be generated from a discharge pressure of the pump 37,as referred to later.

The oil passage L12 branches into two, and one branched is providedthereon with the pressure increase valve 32 for controlling the pressureincrease of the brake hydraulic pressure to the wheel cylinder WC1 forthe rear left wheel 7RL. The other branched is provided thereon with thepressure increase valve 33 for controlling the pressure increase of thebrake hydraulic pressure to the wheel cylinder WC2 for the front rightwheel 7FR. Each of the pressure increase valves 32, 33 is configured asa two-position valve which is controllable by the brake ECU 60 to beswitched into a communication state and a blocked state. Thus, when thepressure increase control valves 32, 33 is held in the communicationstate, each of the wheel cylinders WC1, WC2 can be supplied with eitherthe base hydraulic pressure of the master cylinder 23 or a hydraulicpressure which is made by adding a controlled hydraulic pressure builtby the operation of the pump 37 to the base hydraulic pressure.

Further, the oil passages L12 between the pressure increase controlvalves 32, 33 and the respective wheel cylinders WC1, WC2 are incommunication with a reservoir hole 34 a of the pressure regulationreservoir 34 through respective oil passages L13. The oil passages L13respectively have the pressure reducing valves 35, 36 arranged thereon,each of which is controllable by the brake ECU 60 to be switched into acommunication state and a blocked state.

In a usual operation state that the ABS function is not being executed,the pressure increase control valves 32, 33 remain in the communicationstate, while the pressure reducing control valves 35, 36 remain in theblocked state. With the execution of the ABS control, a pressurereducing mode is executed to close the pressure increase control valves32, 33 and to open the pressure reducing control valves 35, 36. Thus,the operating oil is discharged to the pressure regulation reservoir 34through the oil passages L13, and the hydraulic pressure in the wheelcylinders WC1, WC2 are reduced to prevent the front right wheel 7FR andthe rear left wheel 7RL from becoming a tendency to be locked. In apressure increase mode at the time of the ABS function, the pressureincrease control valves 32, 33 are opened, while the the pressurereducing control valves 35, 36 are closed. Thus, the hydraulic pressurein the wheel cylinders WC1, WC2 is increased to increase the brakeforces of the front right wheel 7FR and the rear left wheel 7RL. Thepressure increase control valves 32, 33 are provided with respectivesafety valves (one-way valves) 32 a, 33 a in parallel thereto. Thesafety valves 32 a, 33 a operate to return the operating fluids in thewheel cylinders WC1, WC2 to the reservoir 24 when the brake pedal 21 isnot stepped further during the ABS function.

Further, the pump 37 together with a safety valve 37 a is arranged on anoil passage L14 which connects the reservoir hole 34 a of the pressureregulation reservoir 34 to the oil passages L12 extending between thehydraulic control valve 31 and the pressure increase control valves 32,33. A damper 38 arranged on the discharge side of the pump 37 absorbsthe pulsation in pressure in the discharged operating oil to urge thesame to be supplied to the oil passages L12 without such pressurepulsation. The suction side of the pump 37 is connected to the reservoirhole 34 a of the pressure regulation reservoir 34. Further, an oilpassage L15 is provided which makes another reservoir hole 34 b of thepressure regulation reservoir 34 communicate with the oil passage L11,so that the pressure regulation reservoir 34 is in communication withthe master cylinder 23.

The pump 37 is able to adjust its discharge flow volume since the drivecurrent to the motor M is regulated by a command from the brake ECU 60.The pump 37 operates at the time of the pressure reducing mode in theABS control and draws the operating oils in the wheel cylinders WC1, WC2or the operating oil in the pressure regulation reservoir 34 to returnthe drawn operating oil to the master cylinder 23 through the hydrauliccontrol valve 31 held in the communication state. Further, the pump 37operates to generate a controlled hydraulic pressure in performing thefunctions that control the vehicle to be stable in posture, such as thetraction control function, the electronic stability control function andthe like, in addition to the active cruise control function and thebrake assist function.

That is, in order to generate a differential pressure across thehydraulic control valve 31 having been switched to the differentialpressure state, the pump 37 draws the operating fluid in the mastercylinder 23 through the oil passage L11 and the oil passage L15 anddischarges the drawn operating fluid to each of the wheel cylinders WC1,WC2 through the oil passages L14, L12 and further through the pressureincrease valves 32, 33 held in the communication state to apply acontrolled hydraulic pressure thereto. Further, also in the case that asufficient regenerative brake force cannot be performed by theregenerative brake device A, and the like, the pump 37 is operated togenerate a differential pressure and applies a controlled hydraulicpressure to each of the wheel cylinders WC1, WC2.

Further, the oil passage L11 is provided thereon with a pressure sensorP for detecting the base hydraulic pressure generated by the mastercylinder 23, and the detected signal is transmitted to the brake ECU 60.The positions of the first and second pistons 23 b, 23 c in the mastercylinder 23 are grasped from the base hydraulic pressure detected by thepressure sensor P, and this makes it possible to know the manipulationamount of the brake pedal 21. The pressure sensor P may be provided onthe oil passage L21 of the second piping passage L2.

Further, the second piping passage L2 in the hydraulic control unit 25takes the same construction as the aforementioned first piping passageL1 and is composed of oil passages L21-L25. The same is true with valvesand the like, and the second piping passage L2 is provided thereon withthe hydraulic control valve 41 and the pressure regulation reservoir 44.One of branching oil passages L22 is provided thereon with the pressureincrease control valve 42 for controlling the pressure increase of thebrake fluid in the wheel cylinder WC3 of the front left wheel 7FL, whilethe other of the branching oil passages L22 is provided thereon with thepressure increase control valve 43 for controlling the pressure increaseof the brake fluid in the wheel cylinder WC4 of the rear right wheel7RR. Further, the pressure reducing control valves 45, 46 are providedon oil passages L23 respectively branching from the oil passages 22, andthe pump 47 is provided on an oil passage L24.

The hydraulic control unit 25 is able to apply the base hydraulicpressure from the master cylinder 23 and the controlled hydraulicpressure which is built by driving the pumps 37, 47 and by controllingthe hydraulic control valves 31, 41, to the wheel cylinders WC1-WC4 ofthe respective wheels 7RL, 7FR, 7FL, 7RR. When supplied with the basehydraulic pressure and the controlled hydraulic pressure, the respectivewheel cylinders WC1-WC4 operate brake means BK1-BK4 to apply a basehydraulic brake force FB and a controlled hydraulic brake force FC toeach of the wheels 7RL, 7FR, 7FL, 7RR. As the brake means BK1-BK4, thereare used disc brakes, drum brakes or the like, in which friction memberslike the brake pads, brake shoes or the like restrict rotations of discrotors, brake drums or the like which are bodily provided on the wheels.

The brake ECU 60 is an electronic controller for controlling the wholeof the vehicle brake system 1 in cooperation with the hybrid ECU 50. Thebrake ECU 60 controls the openings/closings of the valves and the likein the hydraulic control unit 25 and also controls the driving of themotor M to control the pumps 37, 47. Further, the brake ECU 60 isconnected to receive detection signals from the pedal stroke sensor 21 aand the pressure sensor P. Further, the brake ECU 60 is connected toreceive a detection signal form a following distance sensor(vehicle-to-vehicle sensor) 61. The following distance sensor 61 is asensor which uses a laser beam to detect the following distance to avehicle traveling ahead, and the detection signal of the followingdistance is used in executing the active cruise control function.

The brake ECU 60 calculates a driver target brake force FT correspondingto the manipulation amount of the brake pedal 21, subtracts a basehydraulic brake force FB therefrom and distributes the remainder for useas a controlled hydraulic brake force FC and a regenerative brake force(executed regenerative brake force FG). At this time, the brake ECU 60supplies the hybrid ECU 50 with a command indicating the strength of ademand regenerative brake force FR being a target of the regenerativebrake force. The hybrid ECU 50 controls the regenerative brake device Ain response to the command and feeds back an actually generatedregenerative brake force, that is, an executed regenerative brake forceFG. Upon receiving the executed regenerative brake force FG, the brakeECU 60 finally controls the distribution of the controlled hydraulicbrake force FC to each wheel. The hybrid ECU 50 and the brake ECU 60cooperatively control the hydraulic brake device B and the regenerativebrake device A and correspond to the brake control device in the claimedinvention.

Further, the brake ECU 60 has a function of automatically settingcompensation brake forces FD for the respective wheels by itself independence on the vehicle travelling situation and controlling thedistribution thereof, as exemplified hereinafter. For example; in theactive cruise control function, when the detected following distancedecreases, the brake ECU 60 sets the compensation brake forces FD tokeep the following distance longer than a predetermined value. When eachcompensation brake force FD exceeds the driver target brake force FT,the brake ECU 60 executes a control to automatically compensate thedifference. Further, in the brake assist function, when recognizing anemergency braking manipulation from the braking manipulation amount andthe manipulation speed, the brake ECU 60 sets another compensation brakeforce FE which should be added to the driver target brake force FT. Thebrake ECU 60 automatically executes a control to generate a brake forceon which the compensation brake force FE is added to the driver targetbrake force FT.

Heretofore, the brake force being a surplus over the driver target brakeforce FT has been realized as a result that the brake ECU 60 drives thepumps 37, 47 of the hydraulic control unit 25 to increase the controlledhydraulic pressure and hence, to increase the controlled hydraulic brakeforce FC. The present embodiment is designed to make the regenerativebrake device A generate at least a part of the brake force being thesurplus over the driver target brake force FT.

FIG. 3 is a graph showing the operation property of the vehicle brakesystem 1 at an ordinary time. In FIG. 3, the axis of abscissas indicatesthe manipulation amount of the brake pedal, while the axis of ordinatesindicates brake force. The solid line curve in the figure represents thedriver target brake force FT corresponding to the manipulation amount ofthe brake pedal 21, and the broken line curve represents the basehydraulic brake force FB which corresponds to a base hydraulic pressurethe master cylinder 23 generates in correspondence to the manipulationamount of the brake pedal 21. The difference calculated by subtractingthe base hydraulic brake force FB from the driver target brake force FTis distributed to the regenerative brake force (executed regenerativebrake force FG) by the regenerative brake device A and the controlledhydraulic brake force FC by the pump driving, so that the driver targetbrake force FT is controlled to be generated as calculated. Theoperation property in FIG. 3 is stored in the brake ECU 60 in advance asa map in the form of a table or as relational expressions and is used asoccasion arises.

It is to be noted that each of the brake forces is expressed bytwo-uppercase symbols and will hereafter be referred to as that to whicha numeral is suffixed appropriately. The numeral suffixed is for thepurpose of easing the reference to each of particular values of thebrake forces exemplified in the drawings, and the same uppercase symbolsrepresent brake forces of the same kind even if they have differentnumerals suffixed.

Next, description will be made regarding the control operation of thebrake ECU 60 in the first embodiment. FIG. 4 is a flow chart showing thecontrol processing of the brake ECU 60 in the first embodiment, and thecontrol processing will be referred to as the case that the activecruise control function has been in operation. As illustrated, the brakeECU 60 performs an input processing at step S1. Specifically, the brakeECU 60 reads detection signals of the pedal stroke sensor 21 a, thepressure sensor P and the following distance sensor 61 and exchangesinformation with the hybrid ECU 50.

At step S2, the brake ECU 60 obtains a manipulation amount Z1 of thebrake pedal 21 based on the detection signals of the pedal stroke sensor21 a and the pressure sensor P and calculates a driver target brakeamount FT1 corresponding to the manipulation amount Z1 from theoperation property in FIG. 3. Although the detection signals of both ofthe pedal stroke sensor 21 a and the pressure sensor P are used in orderto make the detected manipulation amount Z1 enhanced in accuracy, thedetection signal of either one of the sensors may be used. The drivertarget brake amount FT1 is usually the amount which is calculated takingthe whole vehicle into consideration. However, in the illustratedcontrol processing flow chart, the amount FT1 is considered as theamount per wheel which is obtained by dividing that for the wholevehicle by the number of the wheels. Step 2 corresponds to the drivertarget brake force calculation means or section in the claimedinvention.

Step S3 is executed to calculate compensation brake forces FD1 for therespective wheels 7FR, 7FL, 7RR, 7RL. In the active cruise control (ACC)function, a setting is made for compensation brake forces FD1 thatbecome necessary in dependence on the following distance detected by thefollowing distance sensor 61. Different compensation brake forces FD1may be set for the respective wheels. Step 3 corresponds to thecompensation brake force setting means or section in the claimedinvention.

Sep 4 is executed to calculate compensated target brake forces FU1 forthe respective wheels 7FR, 7FL, 7RR, 7RL. In the active cruise controlfunction, a larger one is selected from the driver target brake forceFT1 and each compensation brake force FD1, and the base hydraulic brakeforce FB1 obtained from FIG. 3 is subtracted from the selected one forceto obtain the compensated target brake force FU1 for each wheel. Thecompensated target brake force FU1 is the brake force which should beundertaken by the executed regenerative brake force FG and thecontrolled hydraulic brake force FC. Step 4 corresponds to the selectioncompensation means or section in the claimed invention.

At step S5, the right side sum SR obtained by adding the compensatedtarget brake forces FU1 for the front and rear right wheels is comparedwith the left side sum SL obtained by adding the compensated targetbrake forces FU1 for the front and rear left wheels. Step S5 correspondsto the left right comparison means or section in the claimed invention.

Step 6 is reached when the both of the sums SR, SL are equal, and thedouble of the right side sum SR is set as a demand regenerative brakeforce FR. Thus, the demand regenerative brake force FR coincides withthe sum of the compensated target brake forces FU1 for the four wheels.If there is a difference between the both of the sums SR, SL at step S5,step S7 is reached, wherein a smaller one of the right side sum SR andthe light side sum SL is doubled to be set as the demand regenerativebrake force FR. Steps S6 and S7 merge at step S8 to deliver the demandregenerative brake force FR to the hybrid ECU 50, that is, to commandthe generator motor 20 to generate the demand regenerative brake forceFR. The generator motor 20 generates as much regenerative brake force aspossible within the demand regenerative brake force FR, and the hybridECU 50 transmits the executed regenerative brake force FG back to thebrake ECU 60.

At step S9, the brake ECU 60 acquires the executed regenerative brakeforce FG which was exerted by the generator motor 20, from the hybridECU 50. At next step S10, the value made by dividing the executedregenerative brake force FG by four (4) is subtracted from therespective compensated target brake forces FU1 for the four wheels toset respective controlled hydraulic brake forces FC1 for the fourwheels. Steps S5-S10 correspond to the distribution control means orsection in the claimed invention. Further, step S6 and steps S8-S10correspond to the left right equal-time distribution control means orsection in the claimed invention, and steps S7-S10 correspond to theleft right unequal-time distribution control means or section in theclaimed invention.

At final step S11, in order to realize the respective controlledhydraulic brake forces FC1 on the four wheels, the brake ECU 60 controlssolenoids of the respective valves in the hydraulic control nit 25 andalso controls the motor M to drive the pumps 37, 47. Thus, one cycle ofthe control processing is completed, and return is made to step S1 torepetitively execute the control processing thereafter.

In the case that the brake assist (BA) function operates, the processingat step S3 and S4 are changed from those aforementioned. That is, atstep S3, an emergency braking manipulation is recognized from themanipulation amount P1 of the brake pedal and the manipulation speedbeing the time-dependant change rate, and a compensation brake force FE1to be added, to the driver target brake force FT1 is set. At step S4,the compensation brake force FE1 is added to the driver target brakeforce FT1, and the base hydraulic brake force FB1 is subtracted from thesum of the addition to set the compensated target brake force FU1 foreach wheel. In this case, step S4 corresponds to the additioncompensation means or section in the claimed invention.

Next, description will be made regarding the operation and effects ofthe vehicle brake system 1 in the first embodiment constructedhereinabove. FIG. 5 is a combination of graphs schematicallyexemplifying the result that the brake ECU executed the controlprocessing shown in FIG. 4 during the operation of the active cruisecontrol function. The upper graph in the figure exemplifies thedistribution of the brake forces to the front right wheel 7FR, while thelower graph represents the compensation brake force FD2 set in theactive cruise control function. The axis of abscissas in the graphs is acommon time axis (t).

FIG. 5 exemplifies the case wherein the stepping of the brake pedal 21begins at time t1, the manipulation amount Z of the pedal 21 isgradually increased until time t3, the manipulation amount Z is keptalmost fixed from time t3 to time t9, the manipulation amount Z isreturned to zero from time t9 to time t10, and the compensation brakeforce FD2 is set during the period from time t4 to time t8. The drivertarget brake force FT2 which varies in correspondence to themanipulation amount Z of the brake pedal 21 is changed to represent atrapezoidal form, as indicated by the solid line. Further, the basehydraulic brake force FB2 which varies in correspondence to themanipulation amount Z of the brake pedal 21 is changed to represent atrapezoidal form lower in height than that of the driver target brakeforce FT2, as indicated by the broken line.

In this case, during each period of the time t1-t4 and time time t8-t10with the compensation brake force FD2 being not set, the compensatedtarget brake force FU2 is calculated by subtracting the base hydraulicbrake force FB2 from the driver target brake force FT2. Further, duringthe period of time t4-t8 with the compensation brake force FD2 being setto be larger than the driver target brake force FT2, the compensatedtarget brake force FU2 is calculated by subtracting the base hydraulicbrake force FB2 from the compensation brake force FD2. In the uppergraph, the range indicated by a declining hatching is undertaken by theexecuted regenerative brake force FG2, and the range indicated by dotsis undertaken by the controlled hydraulic brake force FC2.

As illustrated, the base hydraulic brake force FB2 is generated at thesame time as the driver target brake force FT2 is generated at time t1,and the compensated target brake force FU2 is undertaken by the executedregenerative brake force FG2. When at time t2, the increase of theexecuted regenerative brake force FG2 becomes gentle and unable tofollow the compensated target brake force FU2, the controlled hydraulicbrake force FC2 is generated, in which state time t4 is reached. Theboth of the executed regenerative brake force FG2 and the controlledhydraulic brake force FC2 are being generated at time t4, and when theactive cruise control function is brought into operation at this time tocause the compensated target brake force FU2 to increase abruptly, theincrement is undertaken by the controlled hydraulic brake force FC2.After the time t4, the controlled hydraulic brake force FC2 is replacedby the executed regenerative brake force FG2 which is increasedgradually thereafter, and during the period of time t5-t6, the whole ofthe compensated target brake force FU2 is undertaken by the executedregenerative brake force FG2. As the executed regenerative brake forceFG2 decreases after time t6, a part of the compensated target brakeforce FU2 is undertaken again by the controlled hydraulic brake forceFC2. Further, when the executed regenerative brake force FG2 becomeszero at time t7, the whole of the compensated target brake force FU2 isundertaken by the controlled hydraulic brake force FC2, and this statecontinues unit time t10.

In the present embodiment, when the compensation brake force FD2exceeding the driver target brake force FT2 is set by the active cruisecontrol function, the regenerative brake device A can be used to coveror undertake the range which exceeds the driver target brake force FT2.Heretofore, the hydraulic brake device B has exclusively been used tocover the range exceeding the driver target brake force FT2. In thissense, according to the present embodiment, the efficiency inregeneration can be improved than that in the prior art.

Also in the case of adding a compensation brake force to the drivertarget brake force FT2 in the brake assist function, the presentembodiment operates likewise as described above. Further, without beinglimited to the active cruise control function and the brake assistfunction, the present embodiment operates likewise as described above inthe case where the brake ECU 60 automatically sets a brake force foreach wheel exceeding the driver target brake force FT2.

Next, description will be made regarding a specific method ofcontrolling the distribution of brake forces to the respective wheels7FR, 7FL, 7RR, 7RL. FIGS. 6(A)-6(D) are schematic diagrams forexplaining specific examples of distribution controls in which the leftright equal-time distribution control means or section (step S6 andsteps S8-S10 in FIG. 4) executes the distribution of brake forces to therespective wheels 7FR, 7FL, 7RR, 7RL. FIG. 6(A) indicates thecompensated target brake forces FU3 for the respective wheels 7FR, 7FL,7RR, 7RL, and each of FIGS. 6(B)-6(D) indicates the executedregenerative brake forces FG3 (numerical value at the upper row by eachwheel) and the controlled hydraulic brake forces FC3 (numerical value atthe lower row by each wheel) which were distributed to the respectivewheels.

In the example shown in FIG. 6(A), the compensated target brake forcesFU3 of the respective wheels 7FR, 7FL, 7RR, 7RL are all 2 units. Thus,each of the right side sum SR3 and the left side sum SL3 is 4 units, andthe left right equal-time distribution control means or section is used.The demand regenerative brake force FR3 becomes 8 units which iscalculated by doubling the right side sum SR3 of 4 units. At this time,where the operation condition of the regeneration brake device A is insatisfaction, the executed regenerative brake force FG3 of 8 units whichmeets the demand regenerative brake force FR3 are exerted as the totalon the front right wheel 7FR and the front left wheel 7FL, as shown inFIG. 6(B). Accordingly, the controlled hydraulic brake force FC3 becomesunnecessary.

Further, where the operation condition of the regeneration brake deviceA is mean or moderate, as shown in FIG. 6(C), the regenerative brakeforce of 2 units can be exerted at each of the front right wheel 7FR andthe front left wheel 7FL, so that the executed regenerative brake forceFG3 becomes 4 units. Accordingly, 1 unit which is obtained by dividingthe 4 units of the executed regenerative brake force FG3 by 4 issubtracted from the 2 units of the compensated target brake force FU3for each wheel, so that 1 unit is set as the controlled hydraulic brakeforce FC3 for each wheel 7FR, 7FL, 7RR, 7RL. Further, where theoperation condition of the regeneration brake device A is insufficient,the executed regenerative brake force FG3 becomes zero, as shown in FIG.6(D). Therefore, the controlled hydraulic brake force FC3 for each wheel7FR, 7FL, 7RR, 7RL becomes 2 units as a result of the compensated targetbrake force FU3 remaining as it is without being undertaken by theexecuted regenerative brake force FG3.

FIGS. 7(A)-7(D) are schematic diagrams for explaining specific examplesof distribution controls in which the left right unequal-timedistribution control means or section (steps S7-S10 in FIG. 4) executesthe distribution of brake forces to the respective wheels 7FR, 7FL, 7RR,7RL. FIG. 7(A) indicates the compensated target brake forces FU4 for therespective wheels 7FR, 7FL, 7RR, 7RL, and each of FIGS. 7(B)-7(C)indicates the executed regenerative brake forces FG4 (numerical value atthe upper row by each wheel) and the controlled hydraulic brake forcesFC4 (numerical value at the lower row by each wheel) which weredistributed to the respective wheels.

In the example shown in FIG. 7(A), the compensated target brake forcesFU4 for the front right wheel 7FR and the rear right wheel 7RR are each4 units, and the compensated target brake forces FU4 for the front leftwheel 7FL and the rear left wheel 7RL are each 2 units. Thus, the rightside sum SR4 becomes 8 units, and the left side sum SL4 becomes 4 units,in which case the left right unequal-time distribution control means orsection is used. The executed regenerative brake force FR4 becomes 8units which is calculated by doubling the 4 units of the left side sumSL4 being the sum on the smaller side. At this time, where the operationcondition of the regenerative brake device A is in satisfaction, asshown in FIG. 7(B), the executed regenerative brake force FG4 of 8 unitswhich meets the demand regenerative brake force FR4 can be exerted asthe total on the front right wheel 7FR and the front left wheel 7FL.Then, 2 units obtained by dividing the 8 unit of the executedregenerative brake force by 4 is subtracted from each of the compensatedtarget brake forces FU4 for respective wheels to obtain controlledhydraulic brake forces FC4 for the respective wheels. Accordingly, asthe controlled hydraulic brake forces FC4, 2 units is set for each ofthe front right wheel 7FR and the rear right wheel 7RR, zero is set foreach of the front left wheel 7FL and the rear left wheel 7RL.

Further, where the operation condition of the regeneration brake deviceA is mean or moderate, as shown in FIG. 7(C), the regeneration brakeforce of 2 units can be exerted at each of the front right wheel 7FR andthe front left wheel 7FL, so that the executed regenerative brake forceFG4 becomes 4 units. Then, 1 unit obtained by dividing the 4 units ofthe executed regenerative brake force FG4 by 4 is subtracted from thecompensated target brake force FU4 for each wheel, so that thecontrolled hydraulic brake force FC4 becomes 3 units for each of thefront right wheel 7FR and the rear right wheel 7RR and 1 unit for eachof the front left wheel 7FL and the rear left wheel 7RL. Further, wherethe operation condition of the regeneration brake device A isinsufficient, the executed regenerative brake force FG4 becomes zero, asshown in FIG. 7(D). Therefore, the controlled hydraulic brake force FC4for each wheel 7FR, 7FL, 7RR, 7RL becomes the compensated target brakeforce FU4 for each wheel remaining as it is without being covered by theexecuted regenerative brake force FG4.

As means for applying different controlled hydraulic pressures to thewheel cylinders which are connected to the same piping passage in thehydraulic control unit 25, the brake ECU 60 cyclically controls thoseselected from the valves in the hydraulic control unit 25 to be openedand closed cyclically. For example, with respect to the cylinders 7FR,7RL connected to the first piping passage L1, the following control isexecuted to lower the controlled hydraulic pressure in the wheelcylinder WC2 for the front right wheel 7FR than that in the wheelcylinder WC1 for the rear left wheel 7RL. The pump 37 is driven, thehydraulic control valve 31 is brought into the different pressure state,the pressure increase valve 32 on the wheel cylinder WC1 side is opened,and the pressure reducing control valve 35 is closed. Thus, the fullpressure of the controlled hydraulic pressure built by the pump 37 isapplied to the wheel cylinder WC1. In this state, the pressure increasevalve 33 and the pressure reducing valve 36 on the wheel cylinder WC2side are controlled to be opened and closed cyclically. Thus, theoperating oil flowing from the pressure increase valve 33 to the wheelcylinder WC2 is decreased in comparison with the operating oil flowingto the wheel cylinder side WC1, and at the same time, the operating oiloutflows from the wheel cylinder WC2 to the pressure reducing valve 36.As a result, the controlled hydraulic pressure in the wheel cylinder WC2is controlled to be lower than that in the wheel cylinder WC1. Further,by making the pressure increase valve 33 and the pressure reducing valve36 changed in the rate of the opening period to the closing period, itis possible to variably adjust the controlled hydraulic pressure in thewheel cylinder WC2 with the wheel cylinder WC1 keeping the controlledhydraulic pressure fixed.

In the first embodiment, as exemplified in FIGS. 6(A)-6(D) and7(A)-7(D), it can be realized to supply the generator motor 20 with themaximum executed regenerative brake force FR3, FR4 satisfying thecondition that, where the wheels are divided into those on the rightside and those on the left side, does not provide an excess brake forceon the wheels on either side. Further, it can be realized to adjust thedistribution of the brake forces to the front wheels and the rearwheels, in other words, to the driving wheels and the driven wheels independence on the strength of the executed regenerative brake force FR3,FR4 by the regenerative brake device A. Accordingly, it can be realizedto generate the executed regenerative brake force FR3, FR4 which is themaximum as far as the right side sum SR3, SR4 and the left side sum SL3,SL4 are not changed, so that the efficiency in regeneration canremarkably be enhanced.

Second Embodiment

Next, description will be made regarding a vehicle brake system in asecond embodiment which differs from the first embodiment in thecalculation method for the demand regenerative brake force FR. Thevehicle brake system in the second embodiment takes the same apparatusconstruction as that of the first embodiment shown in FIGS. 1 and 2, butdiffers therefrom in a control processing shown in FIG. 8. FIG. 8 is aflow chart showing the control processing executed by the brake ECU 60in the second embodiment. In the second embodiment, step S5A in FIG. 8replaces steps S5-S7 in FIG. 4, and step S10A in FIG. 8 differs fromstep S10 in details of calculation.

At step S5A in FIG. 8, the brake ECU 60 calculates a demand regenerativebrake force FR5 by multiplying the smallest value of the compensatedtarget brake forces FU1 for the driving wheels (the front right wheel7FR and the front left wheel 7FL) by the number of the driving wheels.Further, at step S10A, the brake ECU 60 calculates respective controlledhydraulic brake forces FC5 by subtracting the executed regenerativebrake force FG5 from each of the compensated target brake forces FU1 forthe wheels 7RL, 7FR, 7FL, 7RR. This calculation is required forsubstantially the driving wheels only. Step S5A and step 8 in FIG. 8correspond to the regeneration demand means or section in the claimedinvention, step 9 corresponds to the regeneration acquire means orsection in the claimed invention, and step 10A corresponds to theregeneration reflecting means or section in the claimed invention.

FIGS. 9(A)-9(D) are explanatory views for showing specific examples ofdistribution controls in which brake forces are distributed to therespective wheels 7FR, 7FL, 7RR, 7RL in the second embodiment. FIG. 9(A)indicates the compensated target brake forces FU6 for the respectivewheels 7FR, 7FL, 7RR, 7RL, and each of FIGS. 9(B)-9(D) indicates theexecuted regenerative brake forces FG6 (numerical value at the upper rowby each wheel) and the controlled hydraulic brake forces FC6 (numericalvalue at the lower row by each wheel) which were distributed to therespective wheels. In the example shown in FIG. 9(A), the compensatedtarget brake forces FU6 for the front right wheel 7FR and the rear rightwheel 7RR are each 4 units, and the compensated target brake forces FU6for the front left wheel 7FL and the rear left wheel 7RL are each 2units. Thus, the smallest value of the compensated target brake forcesFU6 for the driving wheels is 2 units, and since the driving wheels aretwo, the demand regenerative brake force FR5 becomes 4 units.

At this time, where the operation condition for the regenerative brakedevice A is in satisfaction, as shown in FIG. 9(B), the executedregenerative brake force FG6 of 4 units which meet the demandregenerative brake force FR5 can be exerted as the total on the frontright wheel 7FR and the front left wheel 7FL. Then, with respect to thefront right wheel 7FR and the front left wheel 7FL, the respectiveexecuted regenerative brake forces FG6 are subtracted from therespective compensated target brake forces FU6, so that the controlledhydraulic brake force FC6 becomes 2 units for the front right wheel 7FRand zero for the front left wheel 7FL. The controlled hydraulic brakeforces FC6 for the rear right wheel 7RR and the rear left wheel 7RL areset to the respective compensated target brake forces FU6 remaining asthey are without being undertaken by the executed regenerative brakeforce FG6.

Further, where the operation condition for the regenerative brake deviceA is mean or moderate, as shown in FIG. 9(C), the regenerative brakeforce of 1 unit can be exerted at each of the front right wheel 7FR andthe front left wheel 7FL, so that the executed regenerative brake forceFG6 becomes 2 units in total. Further, the controlled hydraulic brakeforce FC6 for the front right wheel 7FR becomes 3 units, and thecontrolled hydraulic brake force FC6 for the front left wheel 7FLbecomes 1 unit. The controlled hydraulic brake forces FC6 for the rearright wheel 7RR and the rear left wheel 7RL are set to the respectivecompensated target brake forces FU6 remaining as they are. Where theoperation condition for the regenerative brake device A is insufficient,the executed regenerative brake force FG6 becomes zero, as shown in FIG.9(D). Accordingly, the controlled hydraulic brake forces FC6 for therespective wheels 7RL, 7FR, 7FL, 7RR are set to the respectivecompensated target brake forces FU6 remaining as they are.

In the second embodiment, as exemplified in FIGS. 9(A)-9(D), it can berealized to supply the generator motor 20 with the maximum demandregenerative brake force FR5 satisfying the condition that does notprovide an excess brake force on the driving wheels. Further, it can berealized to adjust the controlled hydraulic brake force FC6 for thedriving wheels (the front right wheel 7FR and the front left wheel 7FL)in dependence on the regeneration brake fore FG6 exerted by theregenerative brake device A. Accordingly, it can be realized to generatethe executed regenerative brake force which is the maximum as far as thecompensated target brake forces FU6 for the respective wheels 7FR, 7FL,7RR,7RL are not changed, so that the efficiency in regeneration canremarkably be enhanced.

Various features and many of the attendant advantages in the foregoingembodiments will be summarized as follows:

In the vehicle brake system in the foregoing first embodiment typicallyshown in FIGS. 1-5, the brake control device 60, 50 which cooperativelycontrols the hydraulic brake device B and the regenerative brake deviceA selects a larger one of the driver target brake force FT1corresponding to the manipulation amount of the braking manipulationmember 21 and the compensation brake force FD1 set by the brake controldevice 60, 50 itself for each wheel, subtracts the base hydraulic brakeforce FB1 from the selected one brake force to set the compensatedtarget brake force FU1 for each wheel, and distributes the compensatedtarget brake force FU1 to the controlled hydraulic brake force FC foreach wheel and the regenerative brake force FG for each driving wheel.Thus, when the compensation brake force FD1 exceeds the driver targetbrake force FT1, at least a part of the brake force which partcorresponds to the surplus is distributed to the regenerative brakedevice A. This results in bringing the regenerative brake device A intooperation though the same has heretofore not been operated when thecompensation brake forces FD1 set by the brake control device 60, 50itself are generated during the active cruise control function or thelike, and therefore, the efficiency in regeneration can be enhanced.

Also in the vehicle brake system in the foregoing first embodimenttypically shown in FIGS. 1-5, the brake control device 60, 50 whichcooperatively controls the hydraulic brake device B and the regenerativebrake device A adds the driver target brake force FT1 corresponding tothe manipulation amount of the braking manipulation member 21 and thecompensation brake force FE1 set by the brake control device 60, 50itself for each wheel to obtain the sum, subtracts the base hydraulicbrake force FB1 from the sum to set the compensated target brake forceFU1 for each wheel, and distributes the compensated target brake forceFU1 to the controlled hydraulic brake force FC for each wheel and theregenerative brake force FR for each driving wheel. Thus, at least apart of the compensation brake force FU1 is distributed to theregenerative brake device A. This results in bringing the regenerativebrake device A into operation though the same has heretofore not beenoperated when the compensation brake forces FE1 set by the brake controldevice 60, 50 itself are generated during the brake assist function orthe like, and therefore, the efficiency in regeneration can be enhanced.

Also in the vehicle brake system in the foregoing first embodimenttypically shown in FIG. 1-4, the distribution control means or section(steps S5-S10 in FIG. 4) compares the right side sum SR of thecompensated target brake forces FU1 and the left side sum SL of thecompensated target brake forces FU1 and applies the demand regenerativebrake force FR which is obtained by the addition of the compensatedtarget brake forces FU1 for the four wheels, to the generator motor 20if the sums SR, SL are equal, but applies the demand regenerative brakeforce FR which is obtained by doubling the smaller one of the sums SR,SL if the sums SR, SL differ. Further, in either case, the distributioncontrol means or section subtracts the value which is obtained bydividing the executed regenerative brake force FG by 4, from therespective compensated target brake forces FU1 for the four wheels toset the differences as the controlled hydraulic brake forces FC1 for thefour wheels. That is, the distribution control section operates tosupply the generator motor 20 with the executed regenerative brake forceFG which is the maximum as far as the condition is satisfied that, wherethe wheels are divided into those on the right side and those on theleft side, does not provide an excess braking on the wheels on eitherside, and to cover the deficiency in the executed regenerative brakeforce FG which was actually exerted, by the controlled hydraulic brakeforces FC1 for the respective wheels. Accordingly, in generating thecompensation brake forces FD1/FE1 set by the brake control device 60, 59itself, it can be realized to make the executed regenerative brake forceFG become the maximum as far as the right side sum and the left side sumof the compensated target brake forces are not changed, and therefore,the efficiency in regeneration can remarkably be enhanced.

Further, in the vehicle brake system in the foregoing second embodimenttypically shown in FIGS. 1-2 and 8, the distribution control means orsection (steps S5A-S10A in FIG. 8) operates to supply to the generatormotor 20 the demand regenerative brake force FR5 which is calculated bymultiplying the smallest value of the compensated target brake forcesFU1 for the driving wheels 7FL, 7RL by the number of the driving wheels7FL, 7RL, and to distribute the controlled hydraulic brake forces FC5 tothe respective wheels based on the executed regenerative brake force FGwhich was actually exerted by the generator motor 20. That is, thedistribution control section operates to supply to the generator motor20 the demand regenerative brake force FR5 which is the maximum as faras the condition that does not apply an excess braking to the drivingwheels 7FL, 7RL is satisfied, and to cover the deficiency in theexecuted regenerative brake force FG which was actually exerted, by thecontrolled hydraulic brake forces FC5 for the respective wheels.Accordingly, in generating the compensation brake forces FD1/FE1 set bythe brake control device 60, 50 itself, it can be realized to make theexecuted regenerative brake force FG become the maximum as far as thecompensated target brake forces FU1 for the respective wheels are notchanged, and therefore, the efficiency in regeneration can remarkably beenhanced.

Obviously, numerous further modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

1. A vehicle brake system comprising: a hydraulic brake device having amaster cylinder for generating a base hydraulic pressure correspondingto a manipulation amount of a braking manipulation member, a pump forgenerating a controlled hydraulic pressure, and a hydraulic control unitfor adding a base hydraulic brake force corresponding to the basehydraulic pressure and a controlled hydraulic brake force correspondingto the controlled hydraulic pressure to apply the added brake forces towheels; a regenerative brake device for applying a regenerative brakeforce to driving wheels which are included in the wheels and are drivenby a generator motor; and a brake control device for cooperativelycontrolling the hydraulic brake device and the regenerative brakedevice; wherein the brake control device includes: a driver target brakeforce calculation section for calculating a driver target brake forcefor each wheel corresponding to the manipulation amount of the brakingmanipulation member; a compensation brake force setting section forenabling the brake control device to set compensation brake forces forthe respective wheels independently of the driver target brake force; aselection compensation section for selecting a larger one of the drivertarget brake force and the compensation brake force for each wheel andfor subtracting the base hydraulic brake force from the selected onebrake force to set a compensated target brake force for each wheel; anda distribution control section for controlling the compensated targetbrake force for each wheel to be distributed to the controlled hydraulicbrake force for each wheel and the regenerative brake force for eachdriving wheel.
 2. A vehicle brake system comprising: a hydraulic brakedevice having a master cylinder for generating a base hydraulic pressurecorresponding to a manipulation amount of a braking manipulation member,a pump for generating a controlled hydraulic pressure, and a hydrauliccontrol unit for adding a base hydraulic brake force corresponding tothe base hydraulic pressure and a controlled hydraulic brake forcecorresponding to the controlled hydraulic pressure to apply the addedbrake forces to wheels; a regenerative brake device for applying aregenerative brake force to driving wheels which are included in thewheels and are driven by a generator motor; and a brake control devicefor cooperatively controlling the hydraulic brake device and theregenerative brake device; wherein the brake control device includes: adriver target brake force calculation section for calculating a drivertarget brake force for each wheel corresponding to the manipulationamount of the braking manipulation member; a compensation brake forcesetting section for enabling the brake control device to setcompensation brake forces for the respective wheels independently of thedriver target brake force; an addition compensation section for addingthe compensation brake force for each wheel to the driver target brakeforce to obtain a sum and for subtracting the base hydraulic brake forcefrom the sum to set a compensated target brake force for each wheel; anda distribution control section for controlling the compensated targetbrake force for each wheel to be distributed to the controlled hydraulicbrake force for each wheel and the regenerative brake force for eachdriving wheel.
 3. The vehicle brake system as set forth in claim 1,wherein: the wheels are four wheels including two front wheels and tworear wheels; the driving wheels are selected as the two front wheels orthe two rear wheels; and the distribution control section includes: aleft right comparison section for comparing a right side sum made byadding the compensated target brake forces for the front and rear wheelson a right side with a left side sum made by adding the compensatedtarget forces for the front and rear wheel on a left side, each of thecompensated target brake forces being calculated by the selectioncompensation section; a left light equal-time distribution controlsection being operable when the right side sum and the left side sum areequal, for applying to the generator motor a demand regenerative brakeforce which is obtained by the addition of the compensated target brakeforces for the four wheels, acquiring the executed regenerative brakeforce which was executed by the generator motor, and subtracting a valuewhich is obtained by dividing the executed regenerative brake force byfour, from each of the compensated target brake forces for the fourwheels to set respective differences as the respective controlledhydraulic brake forces; and a left light unequal-time distributioncontrol section being operable when the right side sum and the left sidesum differ, for applying to the generator motor a demand regenerativebrake force which is obtained by doubling a smaller one of the rightside sum and the left side sum, acquiring the executed regenerativebrake force which was executed by the generator motor, and subtracting avalue which is obtained by dividing the executed regenerative brakeforce by four, from each of the compensated target brake forces for thefour wheels to set respective differences as the respective controlledhydraulic brake forces.
 4. The vehicle brake system as set forth inclaim 1, wherein the distribution control section includes: aregeneration demand section for applying to the generator motor a demandregenerative brake force calculated by multiplying a smallest value ofthe compensated target brake forces for the driving wheels calculated bythe selection compensation section, by the number of the driving wheels;a regeneration acquisition section for acquiring the executedregenerative brake force which the generator motor executed based on thedemand regenerative brake force; and a regeneration reflecting sectionfor controlling the distribution of the controlled hydraulic brake forceto each wheel based on the executed regenerative brake force.
 5. Thevehicle brake system as set forth in claim 2, wherein: the wheels arefour wheels including two front wheels and two rear wheels; the drivingwheels are selected as the two front wheels or the two rear wheels; andthe distribution control section includes: a left right comparisonsection for comparing a right side sum made by adding the compensatedtarget brake forces for the front and rear wheels on a right side with aleft side sum made by adding the compensated target forces for the frontand rear wheel on a left side, each of the compensated target brakeforces being calculated by the addition compensation section; a leftlight equal-time distribution control section being operable when theright side sum and the left side sum are equal, for applying to thegenerator motor a demand regenerative brake force which is obtained bythe addition of the compensated target brake forces for the four wheels,acquiring the executed regenerative brake force which was executed bythe generator motor, and subtracting a value which is obtained bydividing the executed regenerative brake force by four, from each of thecompensated target brake forces for the four wheels to set respectivedifferences as the respective controlled hydraulic brake forces; and aleft light unequal-time distribution control section being operable whenthe right side sum and the left side sum differ, for applying to thegenerator motor a demand regenerative brake force which is obtained bydoubling a smaller one of the right side sum and the left side sum,acquiring the executed regenerative brake force which was executed bythe generator motor, and subtracting a value which is obtained bydividing the executed regenerative brake force by four, from each of thecompensated target brake forces for the four wheels to set respectivedifferences as the respective controlled hydraulic brake forces.
 6. Thevehicle brake system as set forth in claim 2, wherein the distributioncontrol section includes: a regeneration demand section for applying tothe generator motor a demand regenerative brake force calculated bymultiplying a smallest value of the compensated target brake forces forthe driving wheels calculated by the addition compensation section, bythe number of the driving wheels; a regeneration acquisition section foracquiring the executed regenerative brake force which the generatormotor executed based on the demand regenerative brake force; and aregeneration reflecting section for controlling the distribution of thecontrolled hydraulic brake force to each wheel based on the executedregenerative brake force.